Nikon D3000 Imatest Results

Nikon D3000 Imatest Results

We routinely use Norman Koren's excellent "Imatest" analysis program for quantitative, thoroughly objective analysis of digicam test images. We highly recommend it to our technically-oriented readers, as it's far and away the best, most comprehensive analysis program we've found to date.

My comments below are just brief observations of what we see in the Imatest results. A full discussion of all the data Imatest produces is really beyond the scope of this review: Visit the Imatest web site for a full discussion of what the program measures, how it performs its computations, and how to interpret its output.

Here's some of the results produced by Imatest for the Nikon D3000:

The Nikon D3000 showed pretty good color accuracy, but like the D60 before it, its average saturation is moderately higher than that of its competition. Hue accuracy was very good, with small hue shifts occurring in some colors, notably cyans, yellow-orange, and yellow-green. Average saturation was 117.4% (17.4% oversaturated) and average "delta-C" color error was 5.77 after correction for saturation, which is quite good. (Delta-C is the same as the more commonly referred to delta-E, but delta-C takes into account only color differences, ignoring luminance variation.) Overall, a good (albeit rather vibrant) color response for a DSLR. (It's worth noting that the D3000 has a fine-grained saturation control, that will let you easily dial down the saturation if you prefer more subdued color.) Mouse over the links below the illustration above to compare results with other similarly priced models.

As is true of most interchangeable lens cameras we test, when using the Adobe RGB color space (which provides a much wider gamut, or range of colors that can be expressed), the Nikon D3000 delivers more highly saturated color. Average saturation was 122.8% and average saturation-corrected hue error was 5.73 "delta-C" units, actually slightly more accurate than the sRGB result. Again, mouse over the links below the illustration above to compare results with competing models.

This image shows how the Nikon D3000 actually rendered the colors of the MacBeth chart, compared to a numerically ideal treatment. In each color swatch, the outer perimeter shows the color as actually captured by the camera, the inner square shows the numerically correct color after correcting for the luminance of the photographed chart (as determined by a second-order curve fit to the values of the gray swatches), and the small rectangle inside the inner square shows the numerically correct color, without the luminance correction. This image shows the generally good hue accuracy, as well as a gamma curve that's slightly shifted toward the lower end of the tonal scale. With the exception of the yellow and orange-yellow squares, most of the colors are rendered brighter (higher luminance) than their numerically correct values. This is a fairly common trick in consumer cameras, to produce bright-looking color in their images. The Nikon D3000 goes a bit further in this area than do most consumer SLRs we test, but the earlier D60's color was very popular with consumers, and the D3000 (basically, the D60's replacement) follows that same general formula.

There's a lot in this particular graph, a lot more than we have room to go into here. (This set of plots has also changed a little in the more recent versions of Imatest. Some of the plots that were shown here previously are now shown in other Imatest output. Since we largely focus on the Noise Spectrum plot, we'll only show the graphic above, which includes that plot.)

In comparing these graphs with those from competing cameras, we've found that the Noise Spectrum graph at lower right is the most important. Cameras that manage to shift their noise spectrum to higher frequencies have much finer-grained noise structures, making their noise less visually objectionable. In the graph above, this would show up as a noise spectrum curve that remained higher on the right side, representing higher noise frequencies.

The Nikon D3000 does a pretty good job of keeping a lot of the luminance noise energy (indicated by the black line) up at high frequencies. The line is fairly flat (though we have seen a few better in this class), so the low-ISO luminance noise that's there is quite fine-grained as a result. Chroma noise at low spatial frequencies, though, is higher, especially in the red channel, showing fairly high low-frequency noise bias for a DSLR. When inspecting low ISO D3000 images very closely, you can see blotches of chroma noise in neutral colors, such as the gray patches in the MacBeth chart (see the exaggerated example at right - NOTE that this is zoomed 400% over the original file data, and the tone curve has been stretched quite a bit to reveal the noise). For whatever reason, this increase in low-frequency chroma noise seems to be something of a trend in consumer SLRs lately, as we noticed it in both the Canon XS and XSi, to name just two. The Nikon D3000 falls roughly between the two Canon models just mentioned in this regard.

Above is the same set of noise data at ISO 1,600. Here, the Noise Spectrum graph is shifted quite a bit toward the left-hand, lower-frequency side than it was at ISO 100, coarsening the "grain" of the image noise patterns quite a bit. The red and blue channels still exhibit slightly more noise at the extreme low end of the frequency spectrum, but, are much lower relative to the luminance noise than at lower ISOs, tracking it closely at all but the lowest frequencies. The Nikon D3000's default noise reduction does a pretty good job at keeping chrominance noise in check at higher ISOs, at least relative to luminance noise, although part of the trade-off is higher luminance noise than some of its competitors. (Personally, we find luminance noise much preferable to chroma noise.) Note that even when High ISO Noise Reduction is "Off" (the default, used here), the D3000 still performs a "minimal" amount noise reduction at ISO 1,600 and above.

Here's the same set of noise data at ISO 3,200. Here again, the Noise Spectrum graph is shifted even more toward the left-hand side, coarsening the "grain" of the image noise patterns further. Note the higher noise values in the top-right and lower-left plots as well.

This chart compares the Nikon D3000's luminance noise performance over a range of ISOs against that of similarly priced SLRs, as well as the Nikon D60, the model it replaces. While we continue to show noise plots of this sort because readers ask for them, we each time point out that the noise magnitude is only a small part of the story, the grain pattern being much more important. Here, we can see that the Nikon D3000's luminance noise magnitude starts about average relative to its competition, but increases fairly linearly to levels above the others at higher ISOs. This is partially because default High ISO Noise Reduction is "Off", but that's also true for the D60, which has lower levels above ISO 200. This agrees with our observations that the Nikon D3000's luminance noise is a little higher than the D60's. Do keep in mind these measurements are taken with each camera set at default settings, so the shape or position of the curve could be influenced by the settings you choose to use.

Nikon D3000 Dynamic Range Analysis

A key parameter in a digital camera is its Dynamic Range, the range of brightness that can be faithfully recorded. At the upper end of the tonal scale, dynamic range is dictated by the point at which the RGB data "saturates" at values of 255, 255, 255. At the lower end of the tonal scale, dynamic range is determined by the point at which there ceases to be any useful difference between adjacent tonal steps. Note the use of the qualifier "useful" in there: While it's tempting to evaluate dynamic range as the maximum number of tonal steps that can be discerned at all, that measure of dynamic range has very little relevance to real-world photography. What we care about as photographers is how much detail we can pull out of the shadows before image noise becomes too objectionable. This, of course, is a very subjective matter, and will vary with the application and even the subject matter in question. (Noise will be much more visible in subjects with large areas of flat tints and subtle shading than it would in subjects with strong, highly contrasting surface texture.)

What makes most sense then, is to specify useful dynamic range in terms of the point at which image noise reaches some agreed-upon threshold. To this end, Imatest computes a number of different dynamic range measurements, based on a variety of image noise thresholds. The noise thresholds are specified in terms of f-stops of equivalent luminance variation in the final image file, and dynamic range is computed for noise thresholds of 1.0 (low image quality), 0.5 (medium image quality), 0.25 (medium-high image quality) and 0.1 (high image quality). For most photographers and most applications, the noise thresholds of 0.5 and 0.25 f-stops are probably the most relevant to the production of acceptable-quality finished images, but many noise-sensitive shooters will insist on the 0.1 f-stop limit for their most critical work.

The image below shows the test results from Imatest for an in-camera JPEG file from the Nikon D3000 with a nominally-exposed density step target (Stouffer 4110), and the D3000's settings such as Contrast (0) and Active D-Lighting (Off) at their default positions.

Here, we can see that he tone curve shows pretty good gradation in highlights, but the shadow end trails off more abruptly. Dynamic range at the highest quality level is 7.31 f-stops, with 11.2 f-stops overall (ignoring the indistinct step reported at the deep shadow end). The high quality score is a bit on the low side for an APS-C sensor, and is at least in part because of the Nikon D3000's slightly higher than average noise at default settings. (It does, however, edge out its closest competitor the Canon Rebel XS slightly at all but the lowest quality thresholds in this test.)

Here are the results with Active D-Lighting enabled. As you can see, both the high quality score (7.17 f-stops) and the total dynamic range (10 f-stops) have dropped slightly compared to their levels with Active D-Lighting disabled. This is in part due to the increased noise caused by Active D-Lighting boosting midtones and shadows in an attempt to increase perceptual dynamic range. The technique is quite effective at balancing highlights and shadows in a subject, producing JPEGs that look and print well directly from the camera. Like all such approaches, though, it doesn't actually increase the overall dynamic range of the camera any.

The illustration above shows the results from an Adobe Camera Raw 5.5 converted NEF file, using the Auto setting. (Slightly better results are likely possible with manually tweaking, but we weren't able to do much better.) As can be seen, the score at the highest quality level was much better than the in-camera JPEG, at 8.61 f-stops, while total dynamic range increased just slightly from 11.2 to 11.4 f-stops. A lot of the improvement at the high quality level has to do with the lower noise levels resulting from Adobe Camera Raw's default noise reduction.

Dynamic Range, the bottom line:

The net result was that the Nikon D3000 showed slightly below average dynamic range in its JPEGs when compared against other current APS-C models. However, D3000 RAW (NEF) files processed in Adobe Camera Raw improved Imatest dynamic range scores substantially, placing the D3000 near the top of the range for APS-C models.

To get some perspective, here's a summary of the Nikon D3000's dynamic range performance, and how it compares to other digital SLRs that we also have Imatest dynamic range data for. (Results are arranged in order of decreasing dynamic range at the "High" quality level.):

Comparing the Nikon D3000 to the rest of the field, its higher than average noise for an APS-C model at default settings is responsible for its slightly below average dynamic range score. We're finding that we prefer this approach to cameras that smudge away subtle subject detail just to achieve lower noise levels. - And all that said, the D3000 does better on dynamic range than most other current cameras selling in its price range.

Nikon D3000 Resolution Chart Test Results

The chart above shows consolidated results from spatial frequency response measurements in both the horizontal and vertical axes for an in-camera JPEG. (We used our very sharp Nikkor 60mm f/2.8 Macro lens for this test, as autofocus with our Sigma 70mm f/2.8 Macro reference lens is not supported with the D3000.) The "MTF 50" numbers tend to correlate best with visual perceptions of sharpness, so those are what we focus on here. The uncorrected resolution figures are 1,607 line widths per picture height in the horizontal direction (corresponding to the vertically-oriented edge), and 1,417 lines along the vertical axis (corresponding to the horizontally-oriented edge), for a combined average of 1,512 LW/PH. Correcting to a "standardized" sharpening with a one-pixel radius increased resolution by quite a bit, resulting in an average of 1,873 LW/PH, noticeably lower than the best we've seen for a 10-megapixel camera, but not out of line with its low-end competitors like the Canon XS.

To see what's going on, refer to the plots below, which show the actual edge profiles for both horizontal and vertical edges, in both their original and corrected forms. Here, you can see that fairly conservative in-camera sharpening is applied in the horizontal direction (according to Imatest, undersharpened by 8.46%) , and even less sharpening is applied in the vertical direction (undersharpened by 14.6%). As usual, for the ultimate in sharpness, dial down the camera's internal sharpening to its lowest level and process the resulting images after the fact in Photoshop or other image-processing application to bring out the maximum detail without introducing sharpening artifacts. That said, the Nikon D3000's images take tight (small-radius) sharpening in Photoshop or other image editing software fairly well.